In such a known chuck (known from German OS No. 23,43,723), a plate has a central opening therein and the rotary slide valve has a pivot pin which is received in the opening. The rotary slide valve is secured against axial shifting with respect to the plate by means of a resilient retaining ring (Seeger ring) which engages in the cylinder chamber the pivot pin. This retaining ring is, however, unable to ever create a sealing connection between the mutually facing plane face of the plate and the plane face of the rotary slide valve. Even if during manufacture the most narrow tolerances would be able to be maintained, with time wear would result from the rotary movement of the rotary slide valve with respect to the plate. A sealing connection between the plane face of the plate and the plane face of the rotary slide valve which faces said plate is not assured therewith. However, this sealing connection is particularly important. Furthermore in the known chuck there is provided as a torque coupling a ball which is movable against spring force in an axial opening of the rotary slide valve, and which ball engages a conical recess of the plate and holds the rotary slide valve in ventilating position with respect to the plate. The ventilating opening is in alignment in said ventilating position with a corresponding axial opening of the plate. If a handcrank which engages the engaging means of the rotary slide valve is rotated, then this torque coupling first assures that the rotary slide valve takes along also the plate, the air cylinder, the power amplifier housing which is fixedly connected to said air cylinder and the hollow spindle which is also fixedly connected to the power amplifier housing. In this manner occurs first in a machine vise the feeding of the movable chuck jaw to the workpiece. As soon as same abuts against the workpiece, the torque which is needed for the further rotation of the hollow spindle is increased. The torque coupling disengages and the rotary slide valve is rotated by means of the handcrank relative to the now resting plate. Through this the airsupply opening of the rotary slide will be connected to the axial opening of the plate which terminates in the cylinder chamber, and thus compressed air is supplied into said cylinder chamber to cause the air-operated piston to be moved and to apply an increased force onto the pressure rod through the power amplifier. This manner of functioning is correct in the case of substantially incompressible workpieces. A chucking of flexible workpieces, as for example a sheet metal package is, however, not possible with this known chuck because the torque coupling disengages, as soon as the movable chuck jaw comes to rest on the first workpiece. Furthermore it is also not possible in the case of the known chuck to adjust the achievable maximum clamping pressure in a simple manner.
The basic purpose of the invention is primarily to produce a chuck of the abovementioned type in which without enlargement of the dimensions, be it in radial or axial direction, a perfect seal of the rotary slide valve with respect to the plate without effecting the remaining manner of operation of the chuck is always assured. A further development of the invention has furthermore also the basic purpose of making it possible to clamp flexible workpieces, as for example sheet-metal packages. Furthermore also in a further development of the invention the clamping pressure is adjustable in stages in a simple manner.
The basic purpose is achieved according to the invention by the rotary slide valve being arranged in a sleeve which concentrically surrounds the rotary slide valve and which is connected to the air cylinder at its one end through a fine thread and which is secured against rotation after axial adjustment, which sleeve has at its other end a radially inwardly directed flange or the like and between said flange and the rotary slide valve there is provided an initially tensioned axial ball bearing.
A perfect seal between the plane surface of the rotary slide valve and the face of the plate is assured by this new arrangement. This perfect seal assures a perfect function of the entire chuck. The perfect seal between the two parts avoids an escaping of compressed air and thus an unintentional opening of the chuck or loosening of the workpiece which is chucked with the chuck. By means of the fine thread which is provided between the sleeve and the air cylinder, the initial tension of the axial ball bearing can take place very sensitively independent from any kind of manufacturing tolerances and any play can be excluded and, in addition, however, also the reciprocal rotatability of the plate and rotary slide valve is maintained. Only after adjustment of the initial tension has occurred the air cylinder and the sleeve are secured against rotation so that the initial tension is maintained.
In an advantageous further development of the invention, an axially resilient ring is provided between the flange and the ball bearing. Same assures that even with a certain amount of wear of the plate and the rotary slide valve, at all times a sealing abutment of both parts will occur.
The axially resilient ring is preferably a cup spring. This cup spring can form at the same time one bearing ring of the ball bearing and can be supported with its inner edge on the flange while the rotary slide valve consists of hardened material and has a shoulder on which the balls are directly supported. Through this structure not only the number of individual parts is reduced but also a particularly compact structure is achieved. The rotary slide valve must be hardened at any rate and the cup spring is a hardened part which easily can take the occurring ball bearing loads.
In place of a cup spring, the axially resilient ring can be constructed V-shaped in cross section, can be supported with its apex on the flange of the rotary slide valve and can form with its two V-legs bearing surfaces for the balls while the rotary slide valve consists of hardened material and has a shoulder on which the balls are directly supported. This ring which in cross-section is V-shaped assures at small structural dimensions and with few individual parts an elastic initial pretension between the rotary slide valve and plate.